In the manufacture of thin film printheads for thermal inkjet pens, it has been a common practice to align and bond a metal orifice plate to an adjacent thin film resistor substrate using an adhesive barrier insulating material such as Vacrel.TM. sold by the DuPont Company of Wilmington, Delaware. It has also been a common practice to photolithographically define a plurality of ink firing chambers and ink feed channels in the Vacrel.TM. layer so that each firing chamber therein is aligned with respect to each heater resistor on an underlying thin film resistor substrate and to an orifice opening or group of openings in the adjacent orifice plate. In this manner, the heater resistors may be electrically driven as is well known to heat the ink within each of the firing chambers to boiling and thus cause the ink to be ejected from the orifice openings in the orifice plate and onto an adjacent print medium.
In the past, it has been a common practice to use electroforming processes to electroplate the orifice plate member into a desired geometry before being transported to an orifice plate attachment station. At this location these orifice or nozzle plates are first optically aligned with the thin film resistor substrate and barrier layer thereon and then adhesively bonded to the Vacrel.TM. barrier layer so that the orifice openings in the electroformed orifice plate are precisely aligned with respect to the heater resistors on the thin film resistor substrate. Various types of electroforming processes have been used in the past in the formation of these orifice plates and are disclosed, for example, in U.S. Pat. No. 4,773,971 issued to Si Ty Lam et al, in U.S. Pat. No. 4,675,083 issued to James G. Bearss et al and in U.S. Pat. No. 4,694,308 issued to C. S. Chan et al. All of these above identified patents are assigned to the present assignee and are incorporated herein by reference.
It has also been a common practice to electroplate these orifice plates on a metal surface and up and over the edges of insulating regions or islands on the metal surface so as to form orifice openings having contours which converge toward the surfaces of these insulating regions or islands. These orifice openings normally converge from a large orifice opening at the back of the orifice plate and smoothly into a smaller orifice opening at the front or ink ejection surface of the orifice plate. As is also well known, the preference for using a convergent geometry orifice opening of this type in the fabrication of thermal inkjet printheads is to minimize "gulping" within the orifice plate and adjacent ink firing chambers and thereby in turn reduce cavitation wear on the thermal inkjet printhead heater resistors during the firing of the inkjet pen. A further and more detailed discussion of this problem of gulping and cavitation wear on the heater resistors may be found in the above commonly assigned U.S. Pat. No. 4,694,308 issued to C. S. Chan et al.
Various types of orifice plate alignment and thin film resistor substrate attachment processes and procedures are also disclosed generally in the above referenced patents and are disclosed in more process-related detail describing the overall thin film printhead fabrication techniques and printhead architecture in the Hewlett Packard Journal, Volume 16, No. 5, published May 1985, and also in the Hewlett Packard Journal, Volume 39, No. 4, published August 1988, both incorporated herein by reference.
The orifice plate fabrication process being currently used by the present assignee is disclosed in the above identified U.S. Pat. No. 4,773,971 issued to Si Ty Lam et al and also in a copending application Ser. No. 07/236,890 of Si Ty Lam et al which is a continuation application of U.S. Pat. No. 4,773,971. This issued patent and continuation application of Si Ty Lam et al both disclose electroplating processes for forming thermal inkjet printhead orifice plates wherein various metals are electroformed on selected substrates. These selected substrates or mandrels are grouped into one class comprising selected metal patterns formed on an underlying insulating layer or substrate and in another class comprising selected insulating patterns formed on an underlying metal layer or substrate. Of particular interest in these Lam et al electroforming processes for making these precision architecture orifice plates is an orifice plate fabrication process wherein a durable inorganic dielectric pattern such as silicon carbide, SiC, is formed on an underlying layer of stainless steel which in turn is supported by a thick glass or quartz plate.
Whereas the above orifice plates produced by the electroforming processes disclosed in the above identified U.S. Pat. No. 4,773,971 and copending application Ser. No. 07/236,890 of Si Ty Lam et al have proven to be highly regarded and commercially successful and superior in most aspects of their operational performance, and whereas these Si Ty Lam electroforming processes are capable of producing high precision architecture orifice plates with closely controlled orifice diameters and center-to-center orifice spacings, there are nevertheless certain applications where it is desired to increase the thickness of these orifice plates in order to increase the thickness of the orifice bores therein. This requirement is necessary in certain applications in order to decrease the ink drop spray which is sometimes caused when the "tail" of an ejected drop of ink is swept against one side of a convergent orifice opening as the ink drop is ejected from the outer or ink ejection orifice surface of a thermal inkjet thin film resistor-type printhead. This ink spraying effect is particularly evident in thermal inkjet printhead designs and architectures wherein the heater resistors of the thin film resistor substrate are offset slightly with respect to the orifice opening center line. This heater resistor offset is used in order to compensate for directionality errors which will otherwise occur when the heater resistors are precisely aligned with respect to these orifice opening center lines. This ink drop spray effect in turn produces a visible edge roughness where the ink drop or dot is deposited on an adjacent print medium, and this edge roughness in turn degrades the resolution and print quality of the printed media.